1. Field of Invention
The invention relates to a rotation angle detecting apparatus and a method of detecting a rotation angle.
2. Description of Related Art
Conventionally, an electric-powered driving system has been incorporated into vehicles, including an electric car, as an electric-powered vehicle, and a torque of a drive motor, as an electrically-operated machine, is produced, i.e. a drive motor torque. The drive motor torque is transferred to a driving wheel. In such an electric-powered driving system, the drive motor receives a direct current from a battery and is driven thereby to produce the above-described drive motor torque for driving. The drive motor also receives a torque through the inertia of the electric car to generate a direct current and supply the current to regenerate (recharge) the battery.
In addition, the drive motor has a rotor, as a rotating body, rotatably provided therein. The electrically-operated machine's components are provided radially outside the rotor. The rotor has a pair of magnetic poles composed of N-pole and S-pole permanent magnets, and the components include a stator having stator coils for U-phase, V-phase and W-phase.
Further, as for an electric-powered driving system, which has been incorporated into a hybrid car, as an electric-powered vehicle. The hybrid car transfers a part of the torque of an engine, i.e. an engine torque, to a power generator (a generator/motor) as a first electrically-operated machine and the rest of the torque to a driving wheel. A planetary gear unit includes a sun gear coupled to the power generator, a ring gear coupled to the driving wheel, and a carrier coupled to an engine. Thus, the electric-powered driving system transfers the rotation output from the ring gear and the drive motor as a second electrically-operated machine to the driving wheel to thereby produce a driving force.
In addition, the power generator and the drive motor each have a rotor rotatably provided therein. The electrically-operated machine's components are provided radially outside the rotor. Each rotor has a pair of magnetic poles composed of N-pole and S-pole permanent magnets, and the components include a stator having stator coils for U-phase, V-phase and W-phase.
Furthermore, the electric car is provided with a drive motor controller functioning as an electrically-operated machine controller; whereas the hybrid car is provided with a power generator controller and a drive motor controller functioning as electrically-operated machine controllers. The pulse-width modulation signals of U-phase, V-phase, and W-phase, generated in the electrically-operated machine controllers, are sent to an inverter. The above-mentioned stator coils are respectively supplied with phase currents generated in the inverter, i.e. currents of U-phase, V-phase, and W-phase, whereby the corresponding drive motor is driven to produce a drive motor torque. Further, the power generator is driven to produce a torque of the power generator, i.e., a generator torque.
For this reason, the above-mentioned electric-powered driving systems are each provided with a rotation angle detector circuit in order to detect a magnetic pole's location that is indicative of a position of the rotor of the power generator, the drive motor, etc. Based on the magnetic pole location detected by the rotation angle detector circuit, the power generator, drive motor, etc. is controlled. The rotation angle detector circuit includes a resolver as a rotation angle detecting section, in which a reference signal is sent to the resolver thereby to generate a resolver signal, followed by sending the resolver signal to a R/D converter, performing the feedback control with the feedback control section in the R/D converter, and calculating the rotation angle of the resolver. Thus, the magnetic pole's location, represented by the rotation angle, can be detected.
Moreover, in case of causing the R/D converter to output a rotation angle for each control timing, the load on the CPU of the electrically-operated machine controller is increased when the power generator, the drive motor, etc. are controlled with the CPU. Therefore, a rotation angle output from the RID converter at a given timing is used as a reference location. Thereafter, the amount of change in rotation angle from the reference location is entered from the RID converter and, in the CPU, the amount of change at the given timings are accumulated for the reference location to estimate a rotation angle at each control timing whereby a magnetic pole's location is detected.
Incidentally, the rotation angle detector circuit is provided with an exciting circuit in order to generate a reference signal. The exciting circuit is connected to an excitation-use power source and generates the reference signal based on a voltage of the excitation-use power source, i.e. a power source voltage. However, an instantaneous interruption of the signal system or power source system, for example, an instantaneous break in a resolver signal line for sending a resolver signal to the R/D converter or an instantaneous power-down of the power source, lowers a power source voltage and prevents the resolver signal from being entered into the R/D converter. After that, the recovery of the power source voltage permits the resolver signal to be entered into the R/D converter, while the R/D converter cannot be controlled from the inside.
Therefore, when a given length of time elapses after the power source voltage has recovered, the reference location is acquired again. Then, the amounts of the change are accumulated for the reference location to estimate and detect a rotation angle at each control timing, for example, see JP-A-11-337371.